This invention pertains to veneer clippers, and more particularly to an easily installable, removable and replaceable, resilient, knife-impact cover structure (jacket) for the surface of an anvil roll in a rotary veneer clipper.
A veneer clipper is a machine which is used in plywood plants throughout the world to clip veneer to width, and to clip out defects. Among a rotary veneer clipper's advantages are that it (a) is very simple mechanically, (b) requires minimum maintenance, (c) operates at very high veneer-flow speeds, (d) does not stop the flow of veneer when it produces a cut, (e) is computer controllable, and (f) is very accurate. Most plywood plants, certainly in North America, have adopted the rotary clipper as a machine of choice, and many rotary veneer clippers are also used in other countries of the world.
Such a clipper operates in the following manner. Veneer flows over a bottom anvil roll that is rotating in such a fashion that its peripheral speed is about the same as the speed that veneer is flowing through the machine. Typically, approximately 2-inches above the bottom anvil roll, and above the flowing veneer, is a flexible knife about ¼-inches thick and about 4-inches wide is held in place, stretched along the length of the roll by hydraulic cylinders which connect to the knife through thrust bearings. The knife is sharpened on both long edges, and nominally (when not cutting) is held stationary in generally a “horizontal-plane” position. Another anvil roll essentially exactly the same as the mentioned bottom anvil roll is mounted above the knife, and rotates at the same speed as does the bottom roll, but in the opposite direction.
When it is time to perform a cut, a computer control system controls servo-valves that cause hydraulic motors which are connected to each end of the knife to cause the knife to rotate through 180-degrees. In this rotation, as the knife goes through a “vertical plane” position, and because the top and bottom anvil rolls are adjusted to be closer together than the width of the knife, the knife is squeezed, or forced, through the veneer and into the bottom anvil roll, effecting a cut of the veneer. Because the knife is sharpened on both edges (so that it can cut every 180-degree turn) the knife also cuts into the top anvil roll.
To make such a clipper operate effectively, it has been necessary to make the associated anvil rolls very massive in order to contain and manage the cutting forces that are developed during a cutting operation. Typically, such anvil rolls are made of 9½-inch diameter solid steel. In the case of an 8-foot wide clipper, the steel for one roll weighs about 2,500-pounds.
Obviously a sharp knife for cutting wood cannot be permitted to drive into, and attempt to cut, steel, such as the steel in the anvil rolls. Therefore, it is conventional that anvil rolls are covered with a bonded polyurethane (or urethane) surface covering normally about ¾-inches thick. Such a surface covering has been proven to be very effective, and substantially all clippers employ this approach to protect the sharp edges of the knife, and to furnish suitable opposing “reaction” structures during a cutting operation. Unfortunately, the knife in a clipper does, gradually and eventually, cut away such a surface covering, and as a consequence, anvil rolls must be re-covered from time to time—typically about every about every three to nine months, depending upon machine operating parameters and history.
When it comes time to replace damaged anvil roll covers, the process currently employed is very problematic and often very costly. In addition to the not surprisingly high cost of shipping such large and heavy components back and forth for damaged-cover removal followed by cover replacement, the current process for cover replacement per se is itself quite involved and expensive.
Typically, rolls that are received for recovering are placed in a metal lathe, and the damaged cover material is removed using a sharp tool bit and the usual lathe tool feed mechanism. The roll is then scraped using a carbide tool scraper in the lathe tool holder, and then taken for sandblasting where a suitable hard sandblast material is employed further to clean the roll and to rough-up the surface for subsequent bonding of a new cover.
The sandblasted roll is then surface treated with a special bonding agent glue, and placed in an oven for overnight processing involving preheating to a temperature of over 200-degrees Fahrenheit.
After overnight heating, the roll is appropriately surrounded by a special mold, and urethane for a new cover is poured into a mold to form around the outside roughened surface of the now prepared and cleaned roll. The roll is then placed back in an oven and cooked for a period of about 8-hours, and thereafter removed and returned to the metal lathe machine. In this machine, an appropriate machining operation is then performed to size the outside surface of the new roll covering to the correct outside diameter. The roll is then prepared for return shipment to its owner.
The present invention uniquely addresses this complicated and costly prior art process of anvil roll recovering. As will be more fully explained shortly, the present invention, to address these prior art issues, features a wear-replaceable resilient cover structure for the known-diameter cylindrical surface of an elongate anvil roll having a known length. This cover structure includes (a) an elongate, tubular, cylindrical armature having inside and outside diameters which are each larger than the anvil roll's surface's known diameter, and (b) an elongate, tubular, cylindrical resiliency sleeve which embeddedly receives, and is stabilized by, the mentioned armature, and which possesses inside and outside diameters that are, respectively, less than and greater than those of the mentioned armature. The sleeve's inside diameter is sized to promote non-bonding, but somewhat frictionally resisted, slide-on/slide-off fitment of the armature-stabilized sleeve relative to the anvil roll's cylindrical surface.
The armature and sleeve combination may be prepared as a single, full-length unit which is constructed to cover the entire, intended coverable surface of an anvil roll, or this combinational armature and sleeve structure may be made in modular “sub-lengths” to be placed end-to-end as a “lateral stack” of covering elements ranging over the entire, intended coverable surface of an anvil roll. Preferably, the armature is formed of a perforate material which enables, during “mold-pouring” of the employed resilient sleeve material of the invention, that poured material to flow into and as a continuum through these perforations, thus to produce a very secure and stable embedment of the armature. Preferably, the armature is formed of an expanded perforate metal, and the embedding sleeve is formed of a molded polyurethane material.
These and other features and clear advantages of the structure of the present invention will become more fully apparent as the description thereof which now follows is read in conjunction with the accompanying drawings.